A typical heating or air conditioning system, such as a heat pump, includes an indoor heat exchanger, an outdoor heat exchanger, a compressor, and may include reversing valves to permit switching between heating and cooling modes. The compressor circulates refrigerant through the evaporator and condenser for cooling or heating. Moreover, the level of refrigerant charge in a heat pump apparatus is important in efficient operation of the heat pump apparatus and knowledge of the refrigerant level is important for diagnosing leaks or other problems. Unfortunately, conventional approaches for determining proper refrigerant charge may require complex valve arrangements and other components, and may be cumbersome or unreliable to use.
For example, one approach for determining proper refrigerant charge in a heat pump is disclosed in U.S. Pat. No. 3,153,913 to Brody entitled "Refrigeration System Including Charge Checking Means". The patent discloses a sight glass in a refrigerant charge container which is connected between two heat exchangers of a heat pump. A portion of the refrigerant charge will be stored in the container during the heating cycle, while the container also has a total capacity capable of containing substantially the entire optimum liquid refrigerant charge. The heat pump requires control means for controlling the pressure differential between the two heat exchangers, with a smaller circulating charge being desired on the heating cycle than on the cooling cycle. The container is connected between the indoor heat exchanger and flow restricting means. The container provides means for obtaining a difference in the effective or circulating charge of refrigerant on the heating and cooling cycles of operation of the heat pump.
For checking the charge as disclosed in U.S. Pat. No. 3,153,913, the heat pump is operated in the cooling mode and a normally open valve provided in the line connecting the indoor heat exchanger with container is closed, while a normally closed valve in the charge checking conduit is opened. Closing the valve prevents flow of liquid refrigerant to the indoor heat exchanger. In other words, the liquid refrigerant flowing into the container can no longer flow into the indoor heat exchanger, while any liquid refrigerant contained in the indoor heat exchanger will be evaporated and returned to the compressor through the low pressure conduits.
The refrigerant condensed in the indoor heat exchanger during the charge checking cycle flows through a capillary into the container where it is maintained in a liquid state by pressure. During the charge checking, any liquid refrigerant stored in any lower pressure portion of the system is transferred to the container. In addition, the sight glass is positioned in an upper portion of the container at the location of the desired liquid/gas interface level. Because it may be difficult to observe the liquid/gas interface with positive accuracy, another valve may be closed to prevent reverse flow of refrigerant from the container and the compressor so that a static reading is obtained. After the proper amount of charge is determined, the various valves are returned to their normal operating positions. In addition, the flow restrictor substantially reduces the refrigerant flow through the system during the charge measuring cycle relative to the flow under ordinary operation.
In other words, U.S. Pat. No. 3,153,913 requires operation in the cooling mode, a special container, manipulation of several valves, and other complexities to obtain an indication of a desired liquid/gas interface level relating to the refrigerant charge. The apparatus may be unnecessarily complex and the procedure too cumbersome to be of significant assistance in determining whether the refrigerant charge level is proper.
Other conventional approaches to determining proper refrigerant charge include a complete purge and measured refill of refrigerant for the heat pump apparatus, or the commonplace method of attaching gauges, taking pressure readings, obtaining indoor and outdoor temperatures, and applying the data so obtained to the equipment manufacturer's charging chart, all very cumbersome and time-consuming. Thus, conventional approaches to determining proper refrigerant charge have significant shortcomings in terms of time required, complexity, cost, and reliability.